JPWO2018181823A1 - Solid electrolyte and all-solid secondary battery - Google Patents

Abstract

The solid electrolyte is formed by substituting a part of the elements constituting the mobile ion-containing material, and has an occupied impurity level occupied by electrons in the band gap of the mobile ion-containing material. The charge holding amount per composition formula of the impurity level is equal to or more than the charge holding amount of mobile ions per composition formula of the mobile ion-containing substance.

Description

The present invention relates to a solid electrolyte and an all-solid secondary battery.
Priority is claimed on Japanese Patent Application No. 2017-068912 filed on March 30, 2017, the content of which is incorporated herein by reference.

  The use of flame-retardant polymer electrolytes and ionic liquids as electrolytes for batteries has been studied. However, since both electrolytes contain organic substances, the fear of liquid leakage and ignition in batteries using the same cannot be wiped out.

  On the other hand, an all-solid secondary battery using ceramics as an electrolyte is essentially nonflammable, has high safety, and can eliminate concerns about liquid leakage, liquid exhaustion, and the like. For this reason, all-solid secondary batteries have attracted attention in recent years.

  Various materials have been reported as solid electrolytes for all-solid secondary batteries. For example, Patent Documents 1 to 4 disclose techniques for realizing a solid electrolyte having a wide potential window.

JP 2010-202499 A JP 2010-272344 A JP 2011-070939 A JP 2013-149493 A

  However, in general, when the potential becomes 5 V or more, the oxide solid electrolyte cannot maintain electronic insulation. As a result, self-discharge occurs, and the upper limit of the operating potential of the all-solid secondary battery decreases.

  The present invention has been made in view of the above problems, and has as its object to provide a solid electrolyte having a high upper limit of a potential window.

The present inventor has made intensive studies to solve the above problems.
As a result, by replacing a part of the zirconium phosphate-based solid electrolyte with an element capable of changing the valence, it is possible to suppress the use of the level constituted by zirconium and oxygen for charge compensation during charge and discharge. It has been found that electronic insulation can be maintained and self-discharge can be suppressed. That is, the following means are provided to solve the above problems.

(1) In the solid electrolyte according to the first aspect, the occupied impurity level occupied by electrons, which is formed by substituting a part of the elements constituting the mobile ion-containing substance, of the mobile ion-containing substance. The charge holding amount per composition formula of the occupied impurity level in the band gap is equal to or more than the charge holding amount of mobile ions per composition formula of the mobile ion-containing substance.

(2) The solid electrolyte according to the above aspect, wherein the mobile ion-containing substance is a zirconium phosphate-based solid electrolyte, and a part of the zirconium in the solid electrolyte is selected from the group consisting of V, Nb, Sb, Ta, and Bi. Substituted with at least one selected or a part of phosphorus of the solid electrolyte is substituted with at least one selected from the group consisting of Ge, Mo, W, Cr, Mn, Fe, Se, and Te. You may.

(3) solid electrolyte according to the above aspects, is expressed by the general formula _{Li x Ta y Zr 2-y} M z P 3-z O 12, wherein M is Cr, W, Mn, Fe, Ge, Se, and Te The content of Cr is zCr, the content of W is zW, the content of Mn is zMn, the content of Fe is zFe, the content of Ge is zGe, and the content of Se is at least one selected from the group consisting of: Assuming that the amount is zSe and the content of Te is zTe, z = zCr + zW + zMn + zFe + zGe + zSe + zTe, y + zCr + zW + zMn × 2 + zFe × 2 + zGe + zSe + zTe ≧ 1, 0 ≦ y <1, 0 ≦ z <1.5, where y = z = 0. Excluding) is preferred.

(4) In the solid electrolyte according to the above aspect, 0 ≦ 1−y−zCr−zW−zMn × 2−zFe × 2−zGe−zSe−zTe ≦ x ≦ 1 + y + zCr + zW × 5 + zMn × 3 + zFe × 3 + zGe × 1 + zSe × 2 + zTe It is preferable that x3 be satisfied and y + zCr + zW + zMnx2 + zFex2 + zGe + zSe + zTe ≧ 1 (except that y = z = 0).

(5) The all solid state secondary battery according to the second aspect has the solid electrolyte according to the above aspect.

(6) In the all solid state secondary battery according to the above aspect, the pair of electrode layers and the solid electrolyte layer having the solid electrolyte provided between the pair of electrode layers have a relative density of 80% or more. Is also good.

  The solid electrolyte according to the above embodiment has a high potential window upper limit.

It is a cross section of an all solid state secondary battery concerning a 1st embodiment. FIG. 3 is a diagram illustrating characteristics of a solid electrolyte in which part of zirconium constituting the solid electrolyte is replaced with calcium as a typical element. FIG. 3 is a diagram illustrating characteristics of a solid electrolyte in which part of zirconium constituting the solid electrolyte is replaced with calcium as a typical element. FIG. 3 is a diagram illustrating characteristics of a solid electrolyte in which part of zirconium constituting the solid electrolyte is replaced with calcium as a typical element. FIG. 3 is a diagram illustrating characteristics of a solid electrolyte in which part of zirconium constituting the solid electrolyte is replaced with calcium as a typical element. FIG. 3 is a diagram illustrating characteristics of the solid electrolyte according to the present embodiment in which part of zirconium constituting the solid electrolyte is replaced with manganese, which is an element capable of changing valence. FIG. 3 is a diagram illustrating characteristics of the solid electrolyte according to the present embodiment in which part of zirconium constituting the solid electrolyte is replaced with manganese, which is an element capable of changing valence. FIG. 3 is a diagram illustrating characteristics of the solid electrolyte according to the present embodiment in which part of zirconium constituting the solid electrolyte is replaced with manganese, which is an element capable of changing valence. FIG. 3 is a diagram illustrating characteristics of the solid electrolyte according to the present embodiment in which part of zirconium constituting the solid electrolyte is replaced with manganese, which is an element capable of changing valence. It is a schematic diagram of the band structure of the solid electrolyte substituted by the typical element. It is a schematic diagram of the band structure of the solid electrolyte 3 substituted by the element which can change valence. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with vanadium _{1 + 0.5x V 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with vanadium _{1 + 0.5x V 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with vanadium _{1 + 0.5x V 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with vanadium _{1 + 0.5x V 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with tantalum _{1 + 0.5x Ta 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with tantalum _{1 + 0.5x Ta 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with tantalum _{1 + 0.5x Ta 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4) Li} a part of ₃ zirconium was replaced with tantalum _{1 + 0.5x Ta 0.5 Zr 1.5 (} PO 4) is a diagram of the characteristic change was measured _three. LiZr _{2 (PO 4)} is a _{diagram 3} of a portion of the phosphorus were measured characteristic change of _{Li 1 + 0.5x Zr 2 W 0.5} P 2.5 O 12 was replaced by tungsten. LiZr _{2 (PO 4)} is a _{diagram 3} of a portion of the phosphorus were measured characteristic change of _{Li 1 + 0.5x Zr 2 W 0.5} P 2.5 O 12 was replaced by tungsten. LiZr _{2 (PO 4)} is a _{diagram 3} of a portion of the phosphorus were measured characteristic change of _{Li 1 + 0.5x Zr 2 W 0.5} P 2.5 O 12 was replaced by tungsten. LiZr _{2 (PO 4)} is a _{diagram 3} of a portion of the phosphorus were measured characteristic change of _{Li 1 + 0.5x Zr 2 W 0.5} P 2.5 O 12 was replaced by tungsten. LiZr _{2 (PO 4)} is a diagram part was measured characteristic change of _{Li 1 + 0.5x Zr 2 Mn 0.5} P 2.5 O 12 was replaced with manganese phosphorus _3. LiZr _{2 (PO 4)} is a diagram part was measured characteristic change of _{Li 1 + 0.5x Zr 2 Mn 0.5} P 2.5 O 12 was replaced with manganese phosphorus _3. LiZr _{2 (PO 4)} is a diagram part was measured characteristic change of _{Li 1 + 0.5x Zr 2 Mn 0.5} P 2.5 O 12 was replaced with manganese phosphorus _3. LiZr _{2 (PO 4)} is a diagram part was measured characteristic change of _{Li 1 + 0.5x Zr 2 Mn 0.5} P 2.5 O 12 was replaced with manganese phosphorus _3. It is a figure which shows the state density distribution of the electron for every Li number. It is a figure which shows the state density distribution of the electron for every Li number. It is a figure which shows the state density distribution of the electron for every Li number. It is a figure which shows the state density distribution of the electron for every Li number. It is a figure which shows the state density distribution of the electron for every Li number. It is a figure which shows the state density distribution of the electron for every Li number. It is a figure which shows the state density distribution of the electron for every Li number.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, in order to make the characteristics of the present invention easy to understand, a characteristic portion may be enlarged for convenience. Therefore, the dimensional ratio of each component illustrated in the drawings may be different from the actual one. The materials, dimensions, and the like illustrated in the following description are merely examples, and the present invention is not limited thereto, and can be implemented with appropriate changes without departing from the scope of the invention.

[All-solid secondary battery]
The all-solid-state secondary battery has at least one first electrode layer 1, at least one second electrode layer 2, and a solid electrolyte 3 sandwiched between the first electrode layer 1 and the second electrode layer 2. The first electrode layer 1, the solid electrolyte 3, and the second electrode layer 2 are sequentially laminated to form a laminate 4. The first electrode layer 1 is connected to a terminal electrode 5 provided on one end side, and the second electrode layer 2 is connected to a terminal electrode 6 provided on the other end side.

  One of the first electrode layer 1 and the second electrode layer 2 functions as a positive electrode layer, and the other functions as a negative electrode layer. Hereinafter, the first electrode layer 1 is referred to as a positive electrode layer 1 and the second electrode layer 2 is referred to as a negative electrode layer 2 for easy understanding.

  As shown in FIG. 1, the positive electrode layers 1 and the negative electrode layers 2 are alternately stacked via the solid electrolyte 3. Transfer of mobile ions between the positive electrode layer 1 and the negative electrode layer 2 via the solid electrolyte 3 causes charging and discharging of the all-solid secondary battery 10.

`` Solid electrolyte ''
The solid electrolyte 3 conducts ions between the positive electrode layer 1 and the negative electrode layer 2. The solid electrolyte 3 is an electronic insulator, and does not basically conduct electrons. Electrons generated or lost in the all-solid-state secondary battery due to the conduction of ions are exchanged with an external circuit via the terminal electrode 5. When the electronic insulation of the solid electrolyte 3 is low, the generated or lost electrons conduct inside the solid electrolyte 3. When the electrons self-discharge in the solid electrolyte 3, the number of electrons output to the outside decreases, and the discharge capacity of the all-solid secondary battery 10 decreases.

  The solid electrolyte 3 according to the present embodiment has an occupied impurity level occupied by electrons, formed by substituting a part of the constituent elements, in the band gap of the movable ion-containing substance, and has a composition formula The number of the occupied impurity levels per unit is equal to or more than the charge holding amount of the mobile ions per the composition formula of the mobile ion-containing substance.

  According to this configuration, even if all the mobile ions in the solid electrolyte are desorbed, the electronic insulation can be maintained, so that the upper limit of the potential window can be increased.

  The solid electrolyte 3 is not particularly limited as long as it satisfies the above requirements. For example, any of a zirconium phosphate solid electrolyte, a perovskite solid electrolyte, and a NASICON solid electrolyte may be used. Further, regardless of the type of mobile ions, any of alkali metals, alkaline earth metals, and other multivalent ions may be used.

An example of these solid electrolytes that satisfy predetermined requirements is zirconium phosphate. The zirconium phosphate-based solid electrolyte means a solid electrolyte in which phosphorus, zirconium, and oxygen constitute a main part of a basic skeleton. A representative example is LiZr ₂ (PO ₄ ) ₃ , including a partially substituted one.

  In the solid electrolyte 3, part of phosphorus or zirconium constituting the solid electrolyte is replaced by another element.

  In the solid electrolyte 3 according to the present embodiment, the element that partially substitutes for phosphorus or zirconium is an element that can change its valence. When part of phosphorus or zirconium is replaced by an element capable of changing valence, the level of zirconium or oxygen constituting the basic skeleton can be suppressed from being used for charge compensation during charge and discharge. Insulation can be maintained and self-discharge can be suppressed. Hereinafter, a description will be given based on a specific example.

2A to 2D are diagrams illustrating characteristics of a solid electrolyte in which part of zirconium constituting the solid electrolyte is replaced by calcium, which is a typical element whose valence hardly changes. Specifically, the general formula _{Li 1 + 0.5x Ca 0.5 Zr 1.5} (PO 4) shows the characteristics of the solid electrolyte which is denoted by _3.

  FIG. 2A is a diagram showing a change in potential when the number of Li per composition formula changes, and FIG. 2B is a diagram showing the highest occupied orbital (HOMO) -the lowest unoccupied orbital (LUMO) of the solid electrolyte with respect to the number of Li per composition formula. FIG. 2C is a diagram showing a gap size, FIG. 2C is a diagram showing a valence change of zirconium and calcium constituting the solid electrolyte when the Li number per composition formula changes, and FIG. 2D is a Li per composition formula. It is a figure which shows the valence change of oxygen which comprises a solid electrolyte when a number changes. Zr1, Zr2, and Zr3 mean sites where zirconium exists on the crystal structure.

  When calcium is substituted as shown in FIG. 2B, the HOMO-LUMO gap of the solid electrolyte sharply decreases even if the Li number per composition formula slightly deviates from 2.0. Reducing the HOMO-LUMO gap means that the solid electrolyte is less likely to maintain electronic insulation.

  The reason why the HOMO-LUMO gap is sharply reduced is that electrons of zirconium and oxygen constituting the basic skeleton of the solid electrolyte are used for charge compensation during charge and discharge. When electrons of zirconium or oxygen constituting the basic skeleton are used for charge compensation, carriers are supplied into the solid electrolyte, and the solid electrolyte cannot maintain electronic insulation.

  It can be confirmed from FIGS. 2C and 2D that electrons of zirconium and oxygen constituting the basic skeleton of the solid electrolyte are used for charge compensation during charge and discharge. In FIG. 2C, the valence of Zr1 rapidly changes from around the point where the number of Li contained in the solid electrolyte exceeds 2.0. In FIG. 2D, the valence of oxygen changes from around the point where the number of Li contained in the solid electrolyte falls below 2.0. That is, it can be said that electrons of zirconium and oxygen are used for charge compensation during charge and discharge. As a result, the electronic insulation is reduced.

  The solid electrolyte in the all-solid secondary battery contributes to the transfer of lithium ions between the positive electrode and the negative electrode. Then, the electrons move between the positive electrode and the negative electrode via the terminal electrode and the external terminal. When the electronic insulation of the solid electrolyte cannot be maintained, electrons that should move between the positive electrode and the negative electrode via the terminal electrode and the external terminal move through the solid electrolyte, and thus exchange electrons with the external circuit. , The charged state of the all-solid secondary battery cannot be maintained.

  A solid electrolyte in which part of zirconium constituting the solid electrolyte is replaced by calcium, which is a typical element, can maintain electronic insulation only when the number of Lis per composition formula is around 2.0.

3A to 3D are diagrams illustrating characteristics of the solid electrolyte 3 according to the present embodiment. In the solid electrolyte 3, a part of zirconium is replaced by manganese capable of changing valence. Solid electrolyte 3 shown here is expressed by the general formula _{Li 1 + 0.5x Mn 0.5 Zr 1.5} (PO 4) 3.

  FIG. 3A is a diagram illustrating a change in potential when the number of Li per composition formula changes, and FIG. 3B is a diagram illustrating a magnitude of a HOMO-LUMO gap of the solid electrolyte 3 with respect to the number of Li per composition formula; FIG. 3C is a diagram showing a change in the valence of zirconium and manganese constituting the solid electrolyte 3 when the number of Li per composition formula is changed, and FIG. 3D is a diagram showing the solid electrolyte 3 when the number of Li per composition formula is changed. FIG. 4 is a diagram showing a change in the valence of oxygen constituting oxygen.

  When the manganese is substituted as shown in FIG. 3B, the solid electrolyte 3 maintains a HOMO-LUMO gap of 0.5 eV or more in a wide range of the number of Li per composition formula from about 0.7 to about 2.4. And maintain electronic insulation. This means that the substitution element capable of changing the valence contributes to charge compensation at the time of charge and discharge, and the level of zirconium and oxygen constituting the basic skeleton of the solid electrolyte 3 is used for charge compensation at the time of charge and discharge. This is for suppressing.

  In FIG. 3C, the valence of manganese changes significantly, but the valences of Zr1 to Zr3 do not change significantly. In FIG. 3D, the valence of oxygen does not fluctuate significantly. That is, manganese having a valence change performs charge compensation, and no carrier is supplied into the solid electrolyte 3, so that the solid electrolyte 3 can maintain insulation.

  As a result, the all-solid-state secondary battery using the solid electrolyte 3 according to the present embodiment can maintain electronic insulation even if the number of Lis per composition formula changes significantly.

  The above description can be explained as follows from the viewpoint of the band structure of the solid electrolyte. FIG. 4 is a schematic diagram of a band structure of a solid electrolyte in which a typical element is substituted. As shown in FIG. 4, the solid electrolyte in which the typical elements are substituted has a valence band V and a conduction band C. The valence band V includes a level of an electron orbit including oxygen constituting the basic skeleton of the solid electrolyte, and the conduction band C includes a level of an electron orbit including zirconium constituting the basic skeleton of the solid electrolyte. .

  When the solid electrolyte shown in FIG. 4 has a specific Li number (2.0 per composition formula in FIGS. 2A to 2D), the level L0 corresponding to the Fermi level is equal to the LUMO level and the HOMO level. Exists in between. In this state, a gap exists between the valence band V and the conduction band C, and the solid electrolyte maintains electronic insulation.

  When Li is further added to the solid electrolyte from this state, the LUMO level receives electrons, and the level corresponding to the Fermi level moves from the position L0 to the position L1. On the other hand, when Li escapes from the solid electrolyte, the HOMO level is oxidized. That is, a hole enters the HOMO level, and the position of the Fermi level moves from the position L0 to the position L2. In either case, the band structure will be metallic. As a result, the electronic insulation of the solid electrolyte is rapidly reduced (FIG. 2B), and the range of usable Li number is narrowed (FIG. 2A).

  On the other hand, FIG. 5 is a schematic diagram of the band structure of the solid electrolyte 3 according to the present embodiment, which is replaced with an element capable of changing the valence. As shown in FIG. 5, an unoccupied impurity level 3a, which is not occupied by electrons, and a solid electrolyte in which a valence-changeable element is substituted are placed in a band gap between a valence band V and a conduction band C. And has at least one of the occupied impurity levels 3b.

  As shown in FIG. 5, when Li enters the solid electrolyte in a state where the level corresponding to the Fermi level exists at the position of the symbol L0, the unoccupied impurity level 3a is first reduced, and the unoccupied impurity level 3a is reduced. (The position of the Fermi level shifts from the code L0 to the code L1 ′). On the other hand, in the state where the Fermi level exists at the position of the symbol L0, when electrons escape from the solid electrolyte, the occupied impurity level is first oxidized, and a hole enters the occupied impurity level 3b (the position of the Fermi level changes from the symbol L0 Move to symbol L2 '). Therefore, an energy gap is maintained between the unoccupied impurity level 3a and the LUMO level, or between the occupied impurity level 3b and the HOMO level. As a result, the solid electrolyte 3 can maintain electronic insulating properties (FIG. 3B), and the range of usable Li number is widened (FIG. 3A).

  In the solid electrolyte according to the present embodiment, the number of occupied impurity levels 3b per composition formula is equal to or more than the amount of charge held by movable ions per composition formula of the mobile ion-containing substance. In this case, even if all the mobile ions are desorbed, all the holes to be added can be trapped in the occupied impurity level 3b, and the holes can be prevented from entering the valence band V. Can be maintained.

  As described above, in the solid electrolyte 3 according to the present embodiment, by partially replacing phosphorus or zirconium with an element capable of changing the valence, electrons included in zirconium and oxygen constituting the basic skeleton are subjected to charge compensation during charge and discharge. To be used for the semiconductor device, and electronic insulation can be maintained.

  The valence-changeable element that substitutes for part of phosphorus or zirconium in the solid electrolyte 3 includes V, Cr, Mn, Fe, Nb, Sb, Ta, Bi, Mo, Te, W, Ge, and Se. At least one selected can be used. Substitution with any of these elements can change the valence, so that it is not necessary to use the level of zirconium or oxygen for charge compensation during charge / discharge, so that electronic insulation can be maintained.

  When the element capable of changing valence replaces a part of zirconium, the element capable of changing valence is preferably at least one selected from the group consisting of V, Nb, Sb, Ta, and Bi. When the element capable of changing valence replaces part of phosphorus, the element capable of changing valence is at least one selected from the group consisting of Ge, Mo, W, Cr, Mn, Fe, Se, and Te. Is preferred.

  When a part of zirconium or phosphorus of the solid electrolyte 3 is replaced with these elements, both the unoccupied impurity level 3a and the occupied impurity level 3b are formed between the gap between the valence band V and the conduction band C, respectively. You.

  As described above, the unoccupied impurity level 3a is used for charge compensation during discharging, and the occupied impurity level 3b is used for charge compensation during charging. Since the solid electrolyte 3 has the unoccupied impurity level 3a and the occupied impurity level 3b in a well-balanced manner, the solid electrolyte 3 can maintain electronic insulating properties in both charging and discharging.

The solid electrolyte 3 may specifically be a compound represented by the following general formula (1).
_{Li x Ta y Zr 2-y} M z P 3-z O 12 (zCr the content of Cr, zW the content of W, Zmn the content of Mn, ZFE the content of Fe, the content of Ge The content of zGe and Se is zSe, the content of Te is zTe, and z = zCr + zW + zMn + zFe + zGe + zSe + zTe, 0 ≦ y <1, 0 ≦ z <1, y + zCr + zW + zMn × 2 + zFe × 2 + zGe + zSe + zTe ≧ 1 (1)
Here, M is preferably at least one selected from the group consisting of Cr, W, Mn, Fe, Ge, Se, and Te.

Assuming that the contents of Cr, W, Mn, Fe, Ge, Se, and Te in M are zCr, zW, zMn, zFe, zGe, zSe, and zSe, these contents are represented by the following general formula (2). , (3) are preferably satisfied.
0 ≦ 1-y-zCr-zW-zMn × 2-zFe × 2-zGe-zSe-zTe ≦ x ≦ 1 + y + zCr + zW × 5 + zMn × 3 + zFe × 3 + zGe × 1 + zSe × 2 + zTe × 3 (2)
y + zCr + zW + zMn × 2 + zFe × 2 + zGe + zSe + zTe ≧ 1 (3)

<Positive electrode layer and negative electrode layer>
As shown in FIG. 1, the positive electrode layer 1 has a positive electrode current collector layer 1A and a positive electrode active material layer 1B containing a positive electrode active material. The negative electrode layer 2 has a negative electrode current collector layer 2A and a negative electrode active material layer 2B containing a negative electrode active material.

  The positive electrode current collector layer 1A and the negative electrode current collector layer 2A preferably have high electron conductivity. Therefore, for example, silver, palladium, gold, platinum, aluminum, copper, nickel, or the like is preferably used for the positive electrode current collector layer 1A and the negative electrode current collector layer 2A. Among these substances, copper hardly reacts with the positive electrode active material, the negative electrode active material, and the solid electrolyte. Therefore, when copper is used for the positive electrode current collector layer 1A and the negative electrode current collector layer 2A, the internal resistance of the all-solid secondary battery 10 can be reduced. The materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may be the same or different.

  The positive electrode active material layer 1B is formed on one side or both sides of the positive electrode current collector layer 1A. For example, when the positive electrode layer 1 is formed on the uppermost layer in the stacking direction of the stacked body 4 among the positive electrode layer 1 and the negative electrode layer 2, the opposing negative electrode layer 2 is formed on the uppermost positive electrode layer 1. There is no. Therefore, in the positive electrode layer 1 located at the uppermost layer, the positive electrode active material layer 1B only needs to be on one surface on the lower side in the stacking direction.

  Similarly to the positive electrode active material layer 1B, the negative electrode active material layer 2B is formed on one or both surfaces of the negative electrode current collector layer 2A. When the negative electrode layer 2 is formed as the lowermost layer of the positive electrode layer 1 and the negative electrode layer 2 in the stacking direction of the stacked body 4, the negative electrode active material layer 2 </ b> B in the lowermost negative electrode layer 2 is stacked in the stacking direction. It only needs to be on one side of the upper side.

  Each of the positive electrode active material layer 1B and the negative electrode active material layer 2B contains a positive electrode active material and a negative electrode active material that exchange electrons. In addition, a conductive aid, a binder, and the like may be included. The positive electrode active material and the negative electrode active material are preferably capable of efficiently inserting and removing mobile ions.

As the positive electrode active material and the negative electrode active material, for example, a transition metal oxide or a transition metal composite oxide is preferably used. Specifically, the lithium manganese composite oxide _{Li 2 Mn a Ma 1-a} O 3 (0.8 ≦ a ≦ 1, Ma = Co, Ni), lithium cobaltate (LiCoO _2), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O _4), the general _formula: represented by _{LiNi x Co y Mn z O 2} (x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1) Composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMbPO ₄ (where Mb is at least one element selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr) ), lithium vanadium phosphate _{(Li 3 V 2 (PO 4} ) 3 or _{LiVOPO 4), Li 2 MnO 3} -LiMcO 2 (Mc = Mn, Co, represented by Ni) L Excess solid solution is represented by lithium titanate _{(Li 4 Ti 5 O 12)} , Li s Ni t Co u Al v O 2 (0.9 <s <1.3,0.9 <t + u + v <1.1) Composite metal oxides and the like can be used.

  There is no clear distinction between the active materials constituting the positive electrode active material layer 1B or the negative electrode active material layer 2B. By comparing the potentials of the two compounds, a compound exhibiting a more noble potential can be used as the positive electrode active material, and a compound exhibiting a lower potential can be used as the negative electrode active material.

  The positive electrode current collector layer 1A and the negative electrode current collector layer 2A may include a positive electrode active material and a negative electrode active material, respectively. The content ratio of the active material contained in each current collector layer is not particularly limited as long as it functions as a current collector. For example, the volume ratio of the positive electrode current collector / the positive electrode active material or the negative electrode current collector / the negative electrode active material is preferably in the range of 90/10 to 70/30.

  Since the positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain a positive electrode active material and a negative electrode active material, respectively, the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the negative electrode current collector layer 2A, and the negative electrode active material The adhesion with the layer 2B is improved.

(Terminal electrode)
As shown in FIG. 1, the terminal electrodes 5 and 6 are formed in contact with the side surfaces of the laminate 4 (the exposed surfaces of the end surfaces of the positive electrode layer 1 and the negative electrode layer 2). The terminal electrodes 5 and 6 are connected to external terminals and transfer electrons to and from the laminate 4.

  It is preferable to use a material having high electron conductivity for the terminal electrodes 5 and 6. For example, silver, gold, platinum, aluminum, copper, tin, nickel, gallium, indium, and alloys thereof can be used.

`` Method of manufacturing all solid state secondary battery ''
(Method of manufacturing solid electrolyte)
The solid electrolyte 3 can be produced using a solid-phase reaction method or the like. Specifically, the solid electrolyte 3 can be manufactured by mixing and firing a compound containing phosphorus and zirconium, which constitute the basic skeleton, and a compound containing the element to be replaced. The substitution amount, substitution site, and the like of the element to be substituted can be controlled by adjusting the molar ratio during mixing.

  The composition of the solid electrolyte 3 can be confirmed using X-ray fluorescence (XRF) or high-frequency inductively coupled plasma emission spectroscopy (ICP).

(Formation of laminate)
As a method for forming the laminate 4, a simultaneous firing method may be used, or a sequential firing method may be used.

  The simultaneous firing method is a method in which a material for forming each layer is stacked, and then a stacked body is manufactured by batch firing. The sequential firing method is a method in which each layer is sequentially formed, and a firing step is performed each time each layer is formed. When the simultaneous firing method is used, the laminated body 4 can be formed with fewer working steps as compared with the case where the sequential firing method is used. Further, when the simultaneous firing method is used, the obtained laminate 4 becomes denser than when the sequential firing method is used. Hereinafter, a case where the laminated body 4 is manufactured using the simultaneous firing method will be described as an example.

The simultaneous firing method includes a step of preparing a paste of each material constituting the laminate 4, a step of applying a paste to a base material and drying to form a green sheet, and laminating the green sheets to form a laminated sheet. Co-firing.
First, each material of the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte 3, the negative electrode active material layer 2B, and the negative electrode current collector layer 2A constituting the laminate 4 is made into a paste.

The method of pasting each material is not particularly limited. For example, a paste is obtained by mixing powder of each material with a vehicle. Here, the vehicle is a general term for a medium in a liquid phase. The vehicle includes a solvent and a binder.
According to this method, the paste for the positive electrode current collector layer 1A, the paste for the positive electrode active material layer 1B, the paste for the solid electrolyte 3, the paste for the negative electrode active material layer 2B, and the paste for the negative electrode current collector layer 2A Make it.

  Next, a green sheet is prepared. The green sheet is obtained by applying the prepared paste on a base material such as a PET (polyethylene terephthalate) film, drying the base material if necessary, and then peeling the base material. The method for applying the paste is not particularly limited. For example, known methods such as screen printing, coating, transfer, and doctor blade can be adopted.

  Next, the produced green sheets are stacked in a desired order and in a desired number of layers to form a laminated sheet. When laminating green sheets, alignment, cutting, and the like are performed as necessary. For example, when a parallel or series-parallel battery is manufactured, it is preferable to perform alignment so that the end face of the positive electrode current collector layer and the end face of the negative electrode current collector layer do not coincide, and to stack green sheets.

The laminated sheet may be produced by using a method of producing a positive electrode active material layer unit and a negative electrode active material layer unit described below and laminating them.
First, a solid electrolyte 3 paste is applied on a base material such as a PET film by a doctor blade method, and dried to form a sheet-like solid electrolyte 3. Next, the paste for the positive electrode active material layer 1B is printed on the solid electrolyte 3 by screen printing and dried to form the positive electrode active material layer 1B. Next, the paste for the positive electrode current collector layer 1A is printed on the positive electrode active material layer 1B by screen printing and dried to form the positive electrode current collector layer 1A. Further, a paste for the positive electrode active material layer 1B is printed on the positive electrode current collector layer 1A by screen printing and dried to form the positive electrode active material layer 1B.

Thereafter, the positive electrode active material layer unit is obtained by peeling off the PET film. The positive electrode active material layer unit is a laminated sheet in which solid electrolyte 3 / positive electrode active material layer 1B / positive electrode current collector layer 1A / positive electrode active material layer 1B are laminated in this order.
A negative electrode active material layer unit is manufactured in the same procedure. The negative electrode active material layer unit is a laminated sheet in which solid electrolyte 3 / negative electrode active material layer 2B / negative electrode current collector layer 2A / negative electrode active material layer 2B are laminated in this order.

  Next, one positive electrode active material layer unit and one negative electrode active material layer unit are stacked. At this time, the solid electrolyte 3 of the positive electrode active material layer unit and the negative electrode active material layer 2B of the negative electrode active material layer unit, or the positive electrode active material layer 1B of the positive electrode active material layer unit and the solid electrolyte 3 of the negative electrode active material layer unit come into contact with each other. Are laminated as follows. Thereby, the positive electrode active material layer 1B / the positive electrode current collector layer 1A / the positive electrode active material layer 1B / the solid electrolyte 3 / the negative electrode active material layer 2B / the negative electrode current collector layer 2A / the negative electrode active material layer 2B / the solid electrolyte 3 A laminated sheet laminated in this order is obtained.

  When laminating the positive electrode active material layer unit and the negative electrode active material layer unit, the positive electrode current collector layer 1A of the positive electrode active material layer unit extends only to one end surface, and the negative electrode current collector layer of the negative electrode active material layer unit Each unit is shifted and stacked so that 2A extends only to the other surface. After that, a sheet for the solid electrolyte 3 having a predetermined thickness is further stacked on the surface of the stacked body in which the solid electrolyte 3 does not exist on the surface to form a stacked sheet.

Next, the produced laminated sheets are collectively pressed. The pressure bonding is preferably performed while heating. The heating temperature at the time of press bonding is, for example, 40 to 95 ° C.
The pressed laminated sheet is heated to, for example, 500 ° C. to 750 ° C. in an atmosphere of nitrogen, hydrogen, and steam to remove the binder. Thereafter, they are simultaneously fired at a time to form a laminate 4 made of a sintered body. The firing of the laminated sheet is performed, for example, by heating to 600 ° C. to 1000 ° C. in an atmosphere of nitrogen, hydrogen, and steam. The firing time is, for example, 0.1 to 3 hours.

  In the stacked body 4 made of the sintered body, the relative density of the active material and the solid electrolyte may be 80% or more. The higher the relative density, the easier the diffusion paths of the mobile ions in the crystal are to be connected, and the higher the ion conductivity.

  In the laminate 4 made of the sintered body, an intermediate layer formed by interdiffusion of elements may be included between the electrode layer and the solid electrolyte layer. By including the intermediate layer, the interfacial resistance between different substances can be reduced.

  In the laminated body 4 made of the sintered body, the electrode layer may have a core-shell structure having a core region and a shell region having different metal ion concentrations or oxygen ion concentrations. By having a core-shell structure, electron conductivity can be improved.

  The obtained sintered body (laminate 4) may be placed in a cylindrical container together with an abrasive such as alumina and barrel-polished. Thereby, the corners of the laminate 4 can be chamfered. As another method, the laminate 4 may be polished by sandblasting. This method is preferable because only a specific portion can be cut.

  By forming the terminal electrodes 5 and 6 at the ends of the stacked body 4 manufactured by the above procedure, an all-solid secondary battery can be manufactured. The terminal electrodes 5 and 6 can be manufactured by means such as sputtering.

  As described above, the all-solid-state secondary battery according to the present embodiment has a large upper limit of the potential window. The reason why the upper limit of the potential window is maintained high is that even if all of Li is desorbed, electrons of oxygen need not be used for charge compensation.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, each configuration in each embodiment and a combination thereof are merely examples, and addition and omission of configurations are not deviated from the scope of the present invention. , Substitutions, and other changes are possible.

"Characteristic change of solid electrolyte during charge and discharge"
As shown in FIG. 2A to FIG. 2D and FIG. 3A to FIG. 3D, the characteristics of the solid electrolyte when the number of Li per composition formula is changed include the potential of the solid electrolyte, the HOMO-LUMO gap of the solid electrolyte, and the solid electrolyte. It was confirmed by measuring the valence change of the constituent elements. This measurement result corresponds to a change in the characteristics of the solid electrolyte when the all-solid secondary battery is charged and discharged. These electronic states can be measured according to experimental methods by systematically examining the composition by changing the composition by UV-Vis spectra or ultraviolet photoelectron spectroscopy (UPS) and inverse photoelectron spectroscopy (IPES). According to the simulation, it can be measured by a first-principles simulation using a Vienna Ab initio Simulation Package (VASP), wien2k, PHASE, CASTEP, or the like. In this case, the measurement was performed by a first-principles simulation using a Vienna Ab initio Simulation Package (VASP).

(Example 1-1)
In Example _1-1, it was measured characteristic change of LiZr 2 _{(PO 4) Li} a part of ₃ zirconium was replaced with vanadium _{1 + 0.5x V 0.5 Zr 1.5 (} PO 4) 3. 6A to 6D show the results. FIG. 6A is a diagram illustrating a change in potential when the number of Li per composition formula changes, and FIG. 6B is a diagram illustrating a magnitude of a HOMO-LUMO gap of the solid electrolyte with respect to the number of Li per composition formula. 6C is a diagram showing a change in the valence of zirconium and vanadium constituting the solid electrolyte when the number of Li per composition formula changes, and FIG. 6D shows a solid electrolyte when the number of Li per composition formula changes. It is a figure which shows the valence change of oxygen.

  As shown in FIG. 6B, even when a part of zirconium was replaced with vanadium, the solid electrolyte maintained electronic insulating properties over a wide range of Li number from about 0.2 to about 2.3. This can also be confirmed from the fact that the valences of zirconium and oxygen shown in FIGS. 6C and 6D do not change significantly with changes in the Li number.

(Example 1-2)
In Example 1-2, the characteristic change of Li _{1 + 0.5 ×} Ta _0.5 Zr _1.5 (PO ₄ ) ₃ in which a part of zirconium of LiZr ₂ (PO ₄ ) ₃ was replaced with tantalum was measured. The results are shown in FIGS. 7A to 7D. FIG. 7A is a diagram showing a change in potential when the number of Li per composition formula is changed, and FIG. 7B is a diagram showing the magnitude of the HOMO-LUMO gap of the solid electrolyte with respect to the number of Li per composition formula. 7C is a diagram showing a change in the valence of zirconium and tantalum constituting the solid electrolyte when the number of Li per composition formula changes, and FIG. 7D shows a solid electrolyte when the number of Li per composition formula changes. It is a figure which shows the valence change of oxygen.

  As shown in FIG. 7B, when a part of zirconium was replaced with tantalum, the solid electrolyte maintained electronic insulating properties when the Li number was in the range from about 0.1 to about 1.7. This can also be confirmed from the fact that the valences of zirconium and oxygen shown in FIGS. 7C and 7D do not change significantly with the change in the Li number.

(Example 1-3)
In Example _1-3, were measured characteristic change of LiZr 2 _{(PO 4) 3} of a part of the phosphorus is substituted with tungsten _{Li 1 + 0.5x Zr 2 W 0.5} P 2.5 O 12. 8A to 8D show the results. FIG. 8A is a diagram illustrating a change in potential when the number of Li per composition formula is changed, and FIG. 8B is a diagram illustrating a magnitude of a HOMO-LUMO gap of the solid electrolyte with respect to the number of Li per composition formula. 8C is a diagram showing a change in the valence of zirconium and tungsten constituting the solid electrolyte when the number of Li per composition formula changes, and FIG. 8D is a diagram showing the valence of oxygen constituting the solid electrolyte when the number of Li changes. It is a figure showing a change.

  As shown in FIG. 8B, even when part of phosphorus was replaced with tungsten, the solid electrolyte maintained electronic insulation in the range of Li number from about 0.2 to about 3.8. This can also be confirmed from the fact that the valences of zirconium and oxygen shown in FIGS. 8C and 8D do not change significantly with changes in the Li number.

(Example 1-4)
In Examples _1-4, were measured characteristic change of LiZr 2 _{(PO 4) 3} of a portion of the phosphorus was replaced with manganese _{Li 1 + 0.5x Zr 2 Mn 0.5} P 2.5 O 12. The results are shown in FIGS. 9A to 9D. 9A is a diagram illustrating a change in potential when the number of Li per composition formula changes, and FIG. 9B is a diagram illustrating a magnitude of a HOMO-LUMO gap of the solid electrolyte with respect to the number of Li per composition formula. 9C is a diagram showing a change in the valence of zirconium and manganese constituting the solid electrolyte when the number of Li per composition formula is changed, and FIG. 9D is a diagram showing the valence of oxygen constituting the solid electrolyte when the number of Li is changed. It is a figure showing a change.

  As shown in FIG. 9B, even when part of phosphorus was replaced with manganese, the solid electrolyte maintained electronic insulation in the range where the Li number was around 0 to around 2.3. This can also be confirmed from the fact that the valences of zirconium and oxygen shown in FIGS. 9C and 9D do not change significantly with changes in the Li number.

As described above, when a part of phosphorus or zirconium of LiZr ₂ (PO ₄ ) ₃ is replaced with an element whose valence can be changed, unlike the case where the element is replaced with a typical element shown in FIGS. In the case of (1), the solid electrolyte was able to maintain electronic insulating properties over a wide range even if the Li number greatly fluctuated.

In the case where Li _x Zr ₂ Mn _0.5 P _2.5 O ₁₂ of Example 1-4 was used, the number of Li was 0, 0.5, 1.0, 1.5, 2.0, 2.. FIGS. 10A to 10D and FIGS. 11A to 11C show the distributions of the density of states (DOS) of the electrons at 5, 3.0, respectively.

  Until the Li number is from about 0 to about 2.5, the occupied impurity level exists in the band gap, so that the level constituted by oxygen is not used and the electronic insulating property is maintained. I understand. If the electronic insulating property can be maintained until the Li number becomes 0, Li will not be desorbed any more, and oxidation accompanying the desorption of Li does not occur, so that the upper limit of the potential window becomes very large.

"Band structure of solid electrolyte"
As described above, all of the solid electrolytes shown in Examples 1-1 to 1-4 can maintain electronic insulation over a wide range even when the number of Li changes. On the other hand, the range of Li in which the solid electrolyte can maintain electronic insulating properties differs for each substance. In order to examine this difference, by using the Vienna Ab initio Simulation Package (VASP), the unoccupied impurity level and the occupied impurity level which are several times as large as those of the replacement element are reduced within the band gap. Was formed. Table 1 shows the results.

"Measurement of solid electrolyte"
Samples (sintered tablets of the solid electrolyte) other than the solid electrolytes of Examples 1-1 to 1-5 were prepared, and their occupied impurity levels, electronic conductivity, and upper limit of the potential window were measured. Table 2 shows the composition and measurement results of each sample.

Example 3-1 to 3-9, the solid electrolyte according to Comparative Example 3-1～3-12 _is denoted by _{Li x Ta y Zr 2-y} M z P 3-z O 12. M is at least one selected from the group consisting of Cr, W, Mn, Fe, Ge, Se, and Te. In Table 2, yTa, zCr, zW, zMn, zFe, zGe, zSe, and zTe indicate the contents of Ta, Cr, W, Mn, Fe, Ge, Se, and Te, respectively.

  The electronic conductivity was calculated by preparing a sintered body of the solid electrolyte, measuring a current value flowing when a voltage of 1 V was applied to the sintered body, and using a result of the measurement.

The potential was swept (1 mV / sec) in the range of 1 V to 10 V (vs Li / Li ⁺ ), and the potential when the oxidation current flowed at 10 μA / cm ² or more was set as the upper limit of the potential window.

  Regardless of which element is substituted, when the number of occupied impurity levels per composition formula is equal to or more than the number of Li per composition formula, it can be seen that the upper limit of the potential window is as large as 10 V or more. (Examples 3-1 to 3-9). Conversely, when the number of occupied impurity levels per composition formula is smaller than the number of Li per composition formula (Comparative Examples 3-1, 3-3, 3-6, 3-8, 3-10, 3-12) ) Shows that the upper limit of the potential window is lower than half of Examples 3-1 to 3-9.

  From the above results, since the number of occupied impurity levels exceeding the upper limit of the number of Li in the solid electrolyte is present in the band gap, all the holes generated by the escape of Li from the solid electrolyte are all occupied impurity levels. It is thought to be trapped by. Then, it is considered that the solid electrolyte constituting the all-solid-state secondary battery maintains electronic insulation. This result corresponds well with the result of the simulation.

Li _0.35 La _0.55 TiO ₃ , NaZr ₂ P ₃ O ₁₂ , and Mg _0.5 Zr ₂ P ₃ were used in order to confirm that the effects of the present invention can be achieved by other than zirconium phosphate and lithium-containing oxide. Sintered tablets of O ₁₂ and a solid electrolyte obtained by substituting the elements were prepared, and their occupied impurity levels, electronic conductivity, and upper limit of the potential window were measured. Table 3 shows the composition and measurement results of each sample.

  Regardless of which element is substituted, when the number of occupied impurity levels per composition formula is equal to or more than the charge holding amount of mobile ions per composition formula, the upper limit of the potential window is as large as 10 V or more. (Examples 4-1 to 4-3). Conversely, when the number of occupied impurity levels per composition formula is smaller than the amount of charge of mobile ions per composition formula (Comparative Examples 4-1 to 4-3), the upper limit of the potential window is set to the value obtained in Example 4- It turns out that it is less than half of 1-4-39.

  From the above results, if the number of occupied impurity levels exceeding the charge holding amount of mobile ions in the solid electrolyte exists in the band gap other than zirconium phosphate-based and lithium-containing oxides, all mobile ions are desorbed. It is considered that the electronic insulation can be maintained even when the solid electrolyte is separated, and the self-discharge of the all-solid secondary battery using the solid electrolyte is suppressed.

  According to the present invention, a solid electrolyte having a high upper limit of the potential window can be provided.

  DESCRIPTION OF SYMBOLS 1 ... Positive electrode layer, 1A ... Positive electrode current collector layer, 1B ... Positive electrode active material layer, 2 ... Negative electrode layer, 2A ... Negative electrode current collector layer, 2B ... Negative electrode active material layer, 3 ... Solid electrolyte, 3a ... Unoccupied impurity Levels, 3b occupied impurity levels, 4 laminates, 5, 6 terminal electrodes, 10 solid-state secondary batteries

Claims (6)

An occupied impurity level occupied by electrons, formed by substituting some of the elements constituting the mobile ion-containing substance, within the band gap of the lithium-containing substance,
The solid electrolyte, wherein the occupied impurity level has a charge holding amount per composition formula of the mobile ion-containing substance that is equal to or more than the charge holding amount of mobile ions per composition formula of the mobile ion-containing substance. The mobile ion-containing material is a zirconium phosphate-based solid electrolyte,
Part of zirconium in the solid electrolyte is substituted with at least one selected from the group consisting of V, Nb, Sb, Ta, and Bi, or part of phosphorus in the solid electrolyte is Ge, Mo, W, The solid electrolyte according to claim 1, wherein the solid electrolyte is substituted with at least one selected from the group consisting of Cr, Mn, Fe, Se, and Te. Are written in the general formula _{Li x Ta y Zr 2-y} M z P 3-z O 12,
M is at least one selected from the group consisting of Cr, W, Mn, Fe, Ge, Se, and Te. The content of Cr is zCr, the content of W is zW, and the content of Mn is zMn. The content of Fe is zFe, the content of Ge is zGe, the content of Se is zSe, the content of Te is zTe, z = zCr + zW + zMn + zFe + zGe + zSe + zTe, and 0 ≦ y <1, 0 ≦ z <1.5, y + zCr + zW + zMn × 2 + zFe 3. The solid electrolyte according to claim 1, which satisfies × 2 + zGe + zSe + zTe ≧ 1 (except y = z = 0). 4.   Furthermore, 0 ≦ 1-yzCr-zW-zMn × 2-zFe × 2-zGe-zSe-zTe ≦ x ≦ 1 + y + zCr + zW × 5 + zMn × 3 + zFe × 3 + zGe × 1 + zSe × 2 + zTe × 3 and y + zCr + zW + zMn × 2 + zFe × The solid electrolyte according to claim 3, which satisfies 2 + zGe + zSe + zTe ≧ 1 (however, y = z = 0 is excluded).   An all-solid secondary battery comprising the solid electrolyte according to claim 1.   The all-solid secondary according to claim 5, wherein a pair of electrode layers and a solid electrolyte layer having the solid electrolyte provided between the pair of electrode layers have a relative density of 80% or more. battery.